Textile materials prepared from blends of natural and synthetic fibers are well known. One important way of preparing blends involves the combination of different slivers at the draw frame, and process and equipment arrangements for achieving a uniform blend on a draw frame have been described, for example, in U.S. Pat. Nos. 3,216,064, 3,447,206, and 3,994,046.
For some special purposes, however, a uniform blend is undesirable. For example, in polyester/cotton blend yarns used in preparation of denims, it is very desirable for the cottom fibers to remain at the surface of the yarn with the polyester fibers concentrated at the core. Yarn with a "sheath-core" structure of this type exhibits dyeability features characteristic of cotton and thus can be dyed with indigo to a satisfactory depth of shade. Unfortunately, none of the usual references has addressed the problem of combining natural and synthetic fiber slivers at the draw frame in such a manner as to insure that the natural fiber is located in the "sheath" of the yarn produced.